Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $224.96   10.760%   $249.1657   $249.17   $249.15   $249.20  
  Purchase #2 $24.54   10.516%   $27.1206   $27.12   $27.10   $27.10  
  Purchase #3 $245.64   9.847%   $269.8282   $269.83   $269.85   $269.80  
  Purchase #4 $112.98   6.857%   $120.727   $120.73   $120.75   $120.70  
  Purchase #5 $52.94   5.849%   $56.0365   $56.04   $56.05   $56.00  
  Purchase #6 $105.48   11.814%   $117.9414   $117.94   $117.95   $117.90  
  Purchase #7 $199.87   11.462%   $222.7791   $222.78   $222.80   $222.80  
  7 purchase totals = $966.41       $1,063.5985   $1,063.61   $1,063.65   $1,063.50